Referring to FIG. 1, the display 100 is shown including pixel circuitry 104 and backlighting circuitry 106. The display 100 can include a liquid crystal display. The pixel circuitry 104 includes a large number of pixels, for example, two million pixels, arranged in a matrix of rows and columns. The pixel matrix is driven by pixel drivers. The system controller 102 controls the pixels by way of the pixel drivers. The system controller 102 selects the pixel that is to be illuminated and also provides the image data to that pixel, by way of the pixel drivers.
The system controller 102 also controls the backlighting circuitry 106. The backlighting circuitry 106 provides the backlight in the displays. In many displays, the backlight is provided by one or more cold cathode fluorescent lamps (CCFL). Recently however, display manufacturers are trying to use light emitting diodes (LEDs) for providing the backlight in the displays. The LEDs are generally arranged in multiple strings. Each string contains several LEDs coupled to each other in a series configuration.
The LED strings can be arranged in a number of different configurations. One such configuration is a parallel configuration, as shown in FIG. 2(a). In FIG. 2(a), the LEDs 202 are arranged in the parallel LED strings 204. One end of each of the LED strings 204 is coupled to the drive voltage source 206. The other end of each of the LED strings 204 is coupled to the ground. Another configuration is a crisscross type configuration in which the various LED strings 208 seem intertwined, as shown in FIG. 2(b). The LED strings 204, 208 emit light when currents flow through them, thereby providing the backlight. The current flowing through each LED 202 of a LED string 204 or 208 is the same because the LEDs of the string are coupled in the series configuration.
The current flowing through a LED string 204 or 208 is known as the drive current of the LED 202. The drive current of the LED 202 is typically generated by applying a voltage to one end of the LED string 204 or 208 and coupling the other end of the LED string 204 or 208 to the ground. The voltage applied to the LED string 204 or 208 is known as the drive voltage of the LED string 204 or 208. The drive voltages and the drive currents of the LED strings 204 or 208 are generally managed by a system controller of the device housing the display, for example, the system controller of a television set.
FIG. 3 shows a prior art display 300 including a drive voltage source 302, LED strings 304, 306, 308, 310, 312, 314, 316, 318 and the system controller 340. The LED strings 304, 306, 308, 310, 312, 314, 316 and 318 are coupled to the field effect transistors (FETs) 320, 322, 324, 326, 328, 330, 332 and 334 respectively. The voltage source 302 is coupled at a common node to one end of each LED string 304, 306, 308, 310, 312, 314, 316 and 318. The voltage source 302 provides the same drive voltage to all the LED strings 304, 306, 308, 310, 312, 314, 316 and 318. The voltage source 302 interfaces with the system controller 340. The system controller 340 also interfaces with the FETs 320, 322, 324, 326, 328, 330, 332 and 334.
The system controller 340 controls the level of the drive voltage by way of the voltage source 302. The system controller 340 is also coupled to the gates (G) of the FETs 320, 322, 324, 326, 328, 330, 332 and 334. The system controller 340 selectively couples the LED strings 304, 306, 308, 310, 312, 314, 316 and 318 to the ground by selectively providing gate voltages to the FETs 320, 322, 324, 326, 328, 330, 332 and 334, thereby creating an electrical path between the voltage source 302 and the ground and allowing the drive currents to flow through the LED strings 304, 306, 308, 310, 312, 314, 316 and 318.
Generally, the system controller 340 controls all aspects of the device housing the display, for example, a television set. The system controller 340 of a television set is a sophisticated device that generally includes a high speed central processing unit (CPU) for multitasking and controlling the overall system functions including power management, analog to digital to analog signal conversion, controlling the row and the column drivers for the pixel circuitry, controlling the backlighting circuitry, and interfacing with the receiver that receives the video and audio feed for the various channels. The system controller 340 carries an enormous amount of work load and requires a large amount of memory and a high speed CPU to do the multitasking of that workload. It would desirable to reduce the workload of the system controller 340 and to perform several tasks in parallel in time with the system controller 340. That would provide for a better and flexible display system that requires less memory and processor speed and can be available for performing new tasks.